1. Field of the Invention
The present invention relates to an optical connector and splicer that allow multiple optical fibers to be coupled precisely when connecting or switching operation is performed on lightwave communication systems. The present invention also relates to a method of producing such connector and splicer. The connector is used to detachably couple optical fibers and the splicer is used to permanently couple optical fibers.
2. Prior Art
FIGS. 1A and 1B show the concept of the conventional structure of a multi-fiber optical connector ferrule which uses two guide pins in connecting arrays of coated optical fibers (ribbon fiber). FIG. 1A is a top view of the conventional structure and FIG. 1B is a side view as seen from the side indicated by arrows X.sub.3 --X.sub.3 in FIG. 1A.
In FIGS. 1A and 1B, the numeral 10 denotes an array of coated optical fibers; 11 is an individual bare optical fiber; 21 is a connector ferrule, 22 is a guide pin, and 23 is a guide pin hole into which the guide pin 22 provided on the ferrule 21 is to be inserted.
The multi-fiber optical connector ferrule 21 is entirely formed by plastic molding and features a positioning accuracy of 3-4 .mu.m or below that can be attained by employing precisely dimensioned molds and an appropriate molding technique. The connector ferrule shown in FIGS. 1A and 1B assumes that each of the coated fiber arrays to be connected contains five optical fibers 11 which are arranged linearly at a pitch of 0.3 mm. The guide pins 22 each having a diameter of 0.7 mm.phi. are spaced from each other at a pitch of 3.6 mm.
Simultaneous coupling of the optical fibers 11 can be achieved in the following manner: two guide pins 22 are inserted into guide pin holes 23 formed in one connector ferrule, then inserted into the corresponding holes in the other ferrule which is positioned in registry with the first ferrule. The two ferrules 21 coupled in this way are fixed securely by a suitable means such as a clamp which presses the rear end of each ferrule and the assembly is then accommodated in a cylindrical housing.
The multi-fiber optical connector ferrule 21 is fabricated by die molding, which proceeds as follows: molding pins each having a slightly larger outside diameter than an individual optical fiber 11 and molding rods that are intended to form holes 23 for insertion of guide pins are arranged on a positioning member in a mold; a molding resin is transfermolded into the cavity and left to stand until it cures; subsequently, the molding pins and molding rods are withdrawn so that fiber guide holes and guide pin insertion holes are left behind in the positioning member. The molding resin may be an epoxy resin which can be shaped at low pressures.
Being entirely formed by plastic molding, the prior art multi-fiber optical connector has the following problems.
(1) In plastic molding, variations in the ratio of resin shrinking is unavoidable because of the change in material or variation in the molding pressure and temperature conditions and it is impossible to achieve consistent production with the pitch and position accuracies of the shaped article being held to 1 .mu.m or below;
(2) Long and undistored holes for guiding optical fibers are not easy to form with molding pins whose diameter is as small as 0.125 mm.phi. and the fiber guide hole length that can be attained is within the range of 1 to 2 mm, with extreme difficulty being encountered in making longer holes (.gtoreq.4-5 mm). That is, because of the molding pressure used or the offsetting in the position of molding pins relative to the positioning member, the molding pins will deform to produce deformed optical fiber guide holes, and this will lead to an increased coupling loss due to fiber bending;
(3) Plastic materials do not have high dimensional stability and it is very difficult to ensure that the dimensional change that occurs during molding as a result of moisture absorption or in the face of a change in temperature that amounts to 100.degree. C. (i.e., from -30.degree. C. to +70.degree. C.) will not exceed 1 .mu.m;
(4) Aligned coupling of connector ferrules is accomplished by inserting guide pins into corresponding guide pin holes in the ferrules. However, the guide pin holes which are formed by resin molding are prone to wear or be damaged or otherwise deformed when metal guide pins are inserted into these holes. As a result, dimensions on the submicron order cannot be precisely maintained and great difficulty is encountered in realizing high-precision coupling of optical fibers;
(5) Resins are also subject to much greater thermal expansion than the quartz of which the optical fibers are made and this increases the chance of the occurrence of an increased internal loss as a result of temperature variations; and
(6) Dimensional measurement and evaluation of the manufactured connector ferrule can only be achieved with extreme difficulty because the ferrule which is formed by resin molding has sagging end edges that defy precise measurements on the submicron order.
In order to achieve high-precision coupling of optical fibers with the multi-fiber optical connector of the type described above, the clearance between the guide pin hole 23 and the guide pin 22 is desirably as small as possible and, in the actual connecting operation, it is necessary to use guide pins that provide a clearance of no greater than 1 .mu.m. However, if, as shown in FIG. 2A, the pitch (P1) between two guide pin holes 23 in one ferrule 21 is larger than the pitch P2 between the guide pin holes in the other ferrule by, for example, 4 .mu.m, the end surfaces of the two ferrules will not have perfect contact with each other and some gap g will be left between the two ferrules as shown in FIG. 2B. The amount of gap g produced could be reduced by exerting an increased pressure when coupling the two ferrules but if the pressure applied is excessive, either the ferrule or the guide pins themselves will break.
Further, FIG. 3 is a sectional view of a multi-fiber silicon chip array connector 31 which is conventionally used as an optical fiber connecting member. Two silicon chip guides 32 that are etched on both surfaces are stacked on each other, with optical fibers 11 being aligned on the mating surfaces. A silicon guide plates 33 having coupling guide grooves is fitted onto the other surface of each silicon chip guide 32 and the assembly is fixed with a clip plate (not shown) to secure the coupling of the fibers.
The aforementioned silicon chip array connector of optical fibers has the following problems.
(1) In order to assemble the connector, optical fibers 11 are placed on one etched silicon chip guide 32, and the other silicon chip guide 32 is placed in alignment with the fibers. This process involves much difficulty when multiple optical fibers have to be placed in as many grooves. What is more, any dust particles entrapped between the grooves and the fibers will cause dimensional errors. In short, the conventional silicon chip array connector has problems in association with the ease of assembly and the introduction of dimensional errors during assembly.
(2) Fiber coupling is achieved using guide grooves formed by etching but the coupled fibers must be subsequently clamped with a clip plate. Therefore, the array connector cannot be connected or disconnected or switched to another channel as readily as in the case of ordinary fiber connectors.
(3) Silicon is a hard material but, as the same time, it is brittle and will be readily nicked at side edges to make it difficult to achieve precisely guided coupling of fibers.
(4) The components of the assembled fiber coupling member are simply joined with a clip plate, so that they may separate if exposed to wet heat. In other words, the joint provided by the coupling member is not highly reliable.